I agree with aggierads. Department store bikes are flat out unsafe for ridding in traffic or for dependable transportation. I dont know how they get away with calling some of those things "bikes."

Anyways, if your budget is truly limited just tell the bike shop owner and see if he can do anything. Remember too that when you buy from a local shop then you are also purchasing a certain amount of free labor that will usually include free fitting, adjustments, and sometimes cleanings! Even in the very short term of things a department store bike can often cost a lot more than the price tag because of constant repairs right out of the box! `15 miles is a good size commute, even for a relative veteran. I know you said your in good shape but you are also going to need decent wheels to not destroy yourself everyday doing that ride.

I would also conisder shopping online in your case. Heres a quick road bike that can handle a rack for 299 http://www.bikesdirect.com/products/...ington1_IX.htm

Also, ask your local bike shop if they sell used bikes or know of a used bike retailer in the area. Does you city have a "bicycle kitchen" or other community bicycle shop? I volunteered at one in my city and they would put together reliable machines from donated bicycles and sell them real cheap.

You got a lot of options so don't run to walmart just yet!